Technical Field
[0001] The invention relates to a polyamide-based film, to a process for preparing the same,
and to a cover window and a display device comprising the same.
Background Art
[0002] Polyamide-based polymers are excellent in resistance to friction, heat, and chemicals.
Thus, they are employed in such applications as primary electrical insulation, coatings,
adhesives, resins for extrusion, heat-resistant paintings, heat-resistant boards,
heat-resistant adhesives, heat-resistant fibers, and heat-resistant films.
[0003] Polyamide is used in various fields. For example, polyamide is made in the form of
a powder and used as a coating for a metal or a magnetic wire. It is mixed with other
additives depending on the application thereof. In addition, polyamide is used together
with a fluoropolymer as a painter for decoration and corrosion prevention. It also
plays a role of bonding a fluoropolymer to a metal substrate. In addition, polyamide
is used to coat kitchenware, used as a membrane for gas separation by virtue of its
heat resistance and chemical resistance, and used in natural gas wells for filtration
of such contaminants as carbon dioxide, hydrogen sulfide, and impurities.
[0004] In recent years, polyamide has been developed in the form of a film, which is less
expensive and has excellent optical, mechanical, and thermal characteristics. Such
a polyamide-based film may be applied to display materials for organic light-emitting
diodes (OLEDs) or liquid crystal displays (LCDs), and the like, and to antireflection
films, compensation films, and retardation films if retardation properties are implemented.
[0005] As the use of such a polyamide-based film is expanded indoors and outdoors, the demand
for a polyamide-based film with enhanced mechanical/optical properties and durability
is continuously increasing.
Detailed Description of the Invention
Technical Problem
[0006] An object of the invention is to provide a polyamide-based film that is excellent
in mechanical properties and optical properties, and a cover window and a display
device comprising the same.
[0007] Another object of the invention is to provide a process for preparing a polyamide-based
film that is excellent in mechanical properties and optical properties.
Solution to the Problem
[0008] An embodiment provides a polyamide-based film, which comprises a polyamide-based
polymer and has a light resistance index of 0.660 GPa
-1 or less as represented by the following Equation 1.

[0009] In Equation 1, Y is the modulus of the film, and ΔYI is the rate of change in yellow
index (YI) of the film before and after a light resistance test in which UV rays are
irradiated to the film at 60°C, the UV irradiation is stopped, and water is sprayed
at 50°C.
[0010] Another embodiment provides a process for preparing a polyamide-based film, which
comprises polymerizing a diamine compound and a dicarbonyl compound in an organic
solvent to prepare a solution comprising a polyamide-based polymer; casting the solution
to prepare a gel sheet; and thermally treating the gel sheet.
[0011] Still another embodiment provides a cover window for a display device, which comprises
a polyamide-based film and a functional layer, wherein the polyamide-based film has
a light resistance index of 0.660 GPa
-1 or less as represented by the above Equation 1.
[0012] An embodiment provides a display device, which comprises a display unit; and a cover
window disposed on the display unit, wherein the cover window comprises a polyamide-based
film and a functional layer, and the polyamide-based film has a light resistance index
of 0.660 GPa
-1 or less as represented by the above Equation 1.
Advantageous Effects of the Invention
[0013] As the polyamide-based film according to the invention has a light resistance index
within a predetermined range, its flexibility and optical properties are excellent,
and its color change due to ultraviolet rays can be effectively suppressed.
Brief Description of the Drawing
[0014]
Fig. 1 is a schematic exploded view of a display device according to an embodiment.
Fig. 2 is a schematic perspective view of a display device according to an embodiment.
Fig. 3 is a schematic cross-sectional view of a display device according to an embodiment.
Fig. 4 is a schematic flow diagram of a process for preparing a polyamide-based film
according to an embodiment.
Best Mode for Carrying out the Invention
[0015] Hereinafter, the embodiments will be described in detail with reference to the accompanying
drawings so that those skilled in the art to which the present invention pertains
may easily practice them. However, the embodiments may be implemented in many different
ways and are not limited to those described herein.
[0016] Throughout the present specification, in the case where each film, window, panel,
layer, or the like is mentioned to be formed "on" or "under" another film, window,
panel, layer, or the like, it means not only that one element is directly formed on
or under another element, but also that one element is indirectly formed on or under
another element with other element(s) interposed between them. In addition, the term
on or under with respect to each element may be referenced to the drawings. For the
sake of description, the sizes of individual elements in the appended drawings may
be exaggeratedly depicted and do not indicate the actual sizes. In addition, the same
reference numerals refer to the same elements throughout the specification.
[0017] Throughout the present specification, when a part is referred to as "comprising"
an element, it is understood that other elements may be comprised, rather than other
elements are excluded, unless specifically stated otherwise.
[0018] In the present specification, a singular expression is interpreted to cover a singular
or plural number that is interpreted in context unless otherwise specified.
[0019] In addition, all numbers and expressions related to the quantities of components,
reaction conditions, and the like used herein are to be understood as being modified
by the term "about," unless otherwise indicated.
[0020] The terms first, second, and the like are used herein to describe various elements,
and the elements should not be limited by the terms. The terms are used only for the
purpose of distinguishing one element from another.
[0021] In addition, the term "substituted" as used herein means to be substituted with at
least one substituent group selected from the group consisting of deuterium, -F, -Cl,
-Br, - I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino
group, a hydrazine group, a hydrazone group, an ester group, a ketone group, a carboxyl
group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted
alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted
alkoxy group, a substituted or unsubstituted alicyclic organic group, a substituted
or unsubstituted heterocyclic group, a substituted or unsubstituted aryl group, and
a substituted or unsubstituted heteroaryl group. The substituent groups enumerated
above may be connected to each other to form a ring.
Polyamide-based film
[0022] An embodiment provides a polyamide-based film that is excellent not only in mechanical
properties such as modulus, but also in optical properties in terms of high transmittance,
low haze, and low yellow index, in which the deterioration of its optical properties
is effectively suppressed when it is exposed to UV rays.
[0023] The polyamide-based film according to an embodiment comprises a polyamide-base polymer.
[0024] The polyamide-based film has a light resistance index of 0.660 GPa
-1 or less.

[0025] In Equation 1, Y is the modulus of the film, and ΔYI is the rate of change in yellow
index (YI) of the film before and after a light resistance test in which UV rays are
irradiated to the film at 60°C, the UV irradiation is stopped, and water is sprayed
at 50°C.
[0026] In some embodiments, the light resistance test may be carried out by repeating the
test cycle comprising the ultraviolet irradiation and the water spraying 10 times
or more. For example, the test cycle may be carried out 12 times or more. An Accelerated
Weathering Tester, for example a QUV/Spray manufactured by Q-Lab, may be used to perform
this test.
[0027] For example, the light resistance test cycle may be as follows: light having a wavelength
of 340 nm is irradiated to a film sample at an intensity of 0.63 W/m
2 for 4 hours at 60°C. Then, the UV irradiation is stopped, and the sample is left
at 50°C for 4 hours while water is being sprayed thereat.
[0028] When the ultraviolet rays are irradiated, the ultraviolet rays may be UVA (Ultraviolet
A) and may comprise, for example, electromagnetic waves of 10 to 400 nm. Preferably,
the ultraviolet rays may be near ultraviolet rays having a wavelength of 300 to 400
nm. In some embodiments, the ultraviolet rays may have an intensity of 0.2 to 1 W/m
2, preferably, 0.2 to 0.8 W/m
2, 0.2 to 0.7 W/m
2, 0.4 to 1 W/m
2, 0.4 to 0.8 W/m
2, 0.4 to 0.7 W/m
2, 0.6 to 1 W/m
2, 0.6 to 0.8 W/m
2, or 0.4 to 0.6 W/m
2.
[0029] For example, the ultraviolet irradiation and the water spraying may be carried out
for 1 to 10 hours, respectively. For example, they may be carried out for 2 to 8 hours
or 3 to 6 hours, respectively. In some embodiments, the ultraviolet irradiation and
the water spraying may be carried out for the same time period.
[0030] As the polyamide-based film according to an embodiment satisfies the light resistance
index, optical properties such as transmittance and haze and mechanical properties
such as modulus can be maintained to be excellent even after the severe light resistance
test as described above, and a change in yellow index and color index according to
the CIE Lab color coordinates can be effectively suppressed.
[0031] In some embodiments, the light resistance index may be 0.630 GPa
-1 or less, 0.620 GPa
-1 or less, 0.600 GPa
-1 or less, 0.550 GPa
-1 or less, 0.540 GPa
-1 or less, 0.500 GPa
-1 or less, 0.450 GPa
-1 or less, or 0.410 GPa
-1 or less. In such a case, the film may have excellent modulus, light transmittance,
haze, and the like, and the rate of change in yellow index and the color difference
before and after the light resistance test may be reduced. In some embodiments, the
light resistance index may be 0.100 GPa
-1 or more, 0.150 GPa
-1 or more, or 0.200 GPa
-1 or more.
[0032] In some embodiments, the difference (ΔYI) between the yellow index (YI) after the
light resistance test and the yellow index before the test may be 4.5 or less. Preferably,
ΔYI may be 3.9 or less, 3.8 or less, 3.5 or less, 3.0 or less, or 2.5 or less.
[0033] In some embodiments, the polyamide-based film may have a light resistance color change
index of 1.55 to 1.64 as represented by the following Equation 2. In such a case,
there may be provided a polyamide-based film having excellent modulus, transmittance,
and haze while a deterioration in optical properties due to UV exposure is suppressed.

[0034] In Equation 2, ΔE is the color difference of the film before and after the light
resistance test. The color difference may be defined by the following Equation 3 in
the CIE Lab color coordinates.

[0035] In Equation 3, L
∗, a
∗, and b
∗ are L, a, and b values according to the CIE Lab color coordinates after the light
resistance test, respectively, and L
∗0, a
∗0, and b
∗0 are L, a, and b values according to the CIE Lab color coordinates before the light
resistance test, respectively.
[0036] In some embodiments, the color difference (ΔE) before and after the light resistance
test may be 2.6 or less. Preferably, ΔE may be 2.4 or less, 2.3 or less, 2.0 or less,
or 1.6 or less.
[0037] The polyamide-based film according to an embodiment may have an x-direction refractive
index (n
x) of 1.60 to 1.70, 1.61 to 1.69, 1.62 to 1.68, 1.64 to 1.68, 1.64 to 1.66, or 1.64
to 1.65.
[0038] In addition, the polyamide-based film may have a y-direction refractive index (n
y) of 1.60 to 1.70, 1.61 to 1.69, 1.62 to 1.68, 1.63 to 1.68, 1.63 to 1.66, or 1.63
to 1.64.
[0039] Further, the polyamide-based film may have a z-direction refractive index (n
z) of 1.50 to 1.60, 1.51 to 1.59, 1.52 to 1.58, 1.53 to 1.58, 1.54 to 1.58, or 1.54
to 1.56.
[0040] If the x-direction refractive index, the y-direction refractive index, and the z-direction
refractive index of the polyamide-based film are within the above ranges, when the
film is applied to a display device, its visibility is excellent not only from the
front but also from a lateral side, so that a wide angle of view can be achieved.
[0041] The polyamide-based film according to an embodiment may have an in-plane retardation
(R
o) of 800 nm or less. Specifically, the in-plane retardation (R
o) of the polyamide-based film may be 700 nm or less, 600 nm or less, 550 nm or less,
100 nm to 800 nm, 200 nm to 800 nm, 200 nm to 700 nm, 300 nm to 700 nm, 300 nm to
600 nm, or 300 nm to 540 nm.
[0042] In addition, the polyamide-based film according to an embodiment may have a thickness
direction retardation (R
th) of 5,000 nm or less. Specifically, the thickness direction retardation (R
th) of the polyamide-based film may be 4,800 nm or less, 4,700 nm or less, 4,650 nm
or less, 1,000 nm to 5,000 nm, 1,500 nm to 5,000 nm, 2,000 nm to 5,000 nm, 2,500 nm
to 5,000 nm, 3,000 nm to 5,000 nm, 3,500 nm to 5,000 nm, 4,000 nm to 5,000 nm, 3,000
nm to 4,800 nm, 3,000 nm to 4,700 nm, 4,000 nm to 4,700 nm, or 4,200 nm to 4,650 nm.
[0043] Here, the in-plane retardation (R
o) is a parameter defined by a product (Δn
xy × d) of anisotropy (Δn
xy = | n
x - n
y |) of refractive indices of two mutually perpendicular axes on a film and the film
thickness (d), which is a measure of the degree of optical isotropy and anisotropy.
[0044] In addition, the thickness direction retardation (R
th) is a parameter defined by a product of an average of the two birefringences Δn
xz (= | n
x - n
z |) and Δn
yz (= | n
y - n
z |) observed on a cross-section in the film thickness direction and the film thickness
(d).
[0045] If the in-plane retardation and the thickness direction retardation of the polyamide-based
film are within the above ranges, when the film is applied to a display device, it
is possible to minimize the optical distortion and color distortion and to minimize
the light leakage from a lateral side as well.
[0046] The polyamide-based film may comprise a filler in addition to the polyamide-base
polymer.
[0047] The filler may comprise, for example, an oxide, a carbonate, or a sulfate of metal
or metalloid. For example, the filler may comprise silica, calcium carbonate, barium
sulfate, or the like, but it is not limited thereto.
[0048] The filler may be employed in the form of particles. In addition, the surface of
the filler is not subjected to special coating treatment, and it may be uniformly
dispersed in the entire film.
[0049] As the polyamide-based film comprises the filler, the film can secure a wide angle
of view without a deterioration in the optical properties.
[0050] The filler may have a refractive index of 1.55 to 1.75. Specifically, the refractive
index of the filler may be 1.60 to 1.75, 1.60 to 1.70, 1.60 to 1.68, or 1.62 to 1.65,
but it is not limited thereto.
[0051] If the refractive index of the filler satisfies the above range, the birefringence
values related to n
x, n
y, and n
z can be appropriately adjusted, and the luminance of the film at various angles can
be improved.
[0052] On the other hand, if the refractive index of the filler is outside the above range,
there may arise a problem in that the filler is visually noticeable on the film or
that the haze is increased due to the filler.
[0053] The content of the filler may be 100 ppm to 3,000 ppm based on the total weight of
the solids content of the polyamide-based polymer. Specifically, the content of the
filler may be 100 ppm to 2,500 ppm, 100 ppm to 2,200 ppm, 200 ppm to 2,500 ppm, 200
ppm to 2,200 ppm, 250 ppm to 2,100 ppm, or 300 ppm to 2,000 ppm, based on the total
weight of the solids content of the polyamide-based polymer, but it is not limited
thereto.
[0054] If the content of the filler is outside the above range, the haze of the film is
steeply increased, and the filler may aggregate with each other on the surface of
the film, so that a feeling of foreign matter may be visually observed, or it may
cause a trouble in the sliding performance or deteriorate the windability in the preparation
process.
[0055] The content of residual solvents in the polyamide-based film may be 1,500 ppm or
less. For example, the content of residual solvents may be 1,200 ppm or less, 1,000
ppm or less, 800 ppm or less, or 500 ppm or less, but it is not limited thereto.
[0056] The residual solvent refers to a solvent that has not been volatilized during the
film production and remains in the film finally produced.
[0057] If the content of the residual solvents in the polyamide-based film exceeds the above
range, the durability of the film may be deteriorated, and it may have an impact on
the luminance.
[0058] When the polyamide-based film according to an embodiment based on a thickness of
50 µm is folded to have a radius of curvature of 3 mm, the number of folding before
the fracture may be 200,000 or more.
[0059] The number of folding is one when the film is folded to have a radius of curvature
of 3 mm and then unfolded.
[0060] As the number of folding of the polyamide-based film satisfies the above range, it
can be advantageously applied to a foldable display device or a flexible display device.
[0061] The polyamide-based film according to an embodiment may have a surface roughness
of 0.01 µm to 0.07 µm. Specifically, the surface roughness may be 0.01 µm to 0.07
µm or 0.01 µm to 0.06 µm, but it is not limited thereto.
[0062] As the surface roughness of the polyamide-based film satisfies the above range, it
may be advantageous for achieving high luminance even when the angle from the normal
direction of a surface light source is increased.
[0063] The polyamide-based film comprises a polyamide-base polymer. The polyamide-based
polymer may comprise an amide repeat unit. In some embodiments, the polyamide-based
polymer may optionally comprise an imide repeat unit.
[0064] The polyamide-based polymer may be prepared by simultaneously or sequentially reacting
reactants that comprise a diamine compound and a dicarbonyl compound. Specifically,
the polyamide-based polymer may be prepared by polymerizing a diamine compound and
a dicarbonyl compound.
[0065] Alternatively, the polyamide-based polymer is prepared by polymerizing a diamine
compound, a dianhydride compound, and a dicarbonyl compound. Here, the polyamide-based
polymer may comprise an imide repeat unit derived from the polymerization of the diamine
compound and the dianhydride compound and an amide repeat unit derived from the polymerization
of the diamine compound and the dicarbonyl compound.
[0066] The diamine compound is a compound that forms an imide bond with the dianhydride
compound and forms an amide bond with the dicarbonyl compound, to thereby form a copolymer.
[0067] The diamine compound is not particularly limited, but it may be, for example, an
aromatic diamine compound that contains an aromatic structure. For example, the diamine
compound may be a compound represented by the following Formula 1.
[Formula 1] H
2N-(E)
e -NH
2
[0068] In Formula 1, E may be selected from a substituted or unsubstituted divalent C
6-C
30 aliphatic cyclic group, a substituted or unsubstituted divalent C
4-C
30 heteroaliphatic cyclic group, a substituted or unsubstituted divalent C
6-C
30 aromatic cyclic group, a substituted or unsubstituted divalent C
4-C
30 heteroaromatic cyclic group, a substituted or unsubstituted C
1-C
30 alkylene group, a substituted or unsubstituted C
2-C
30 alkenylene group, a substituted or unsubstituted C
2-C
30 alkynylene group, -O-, -S-, -C(=O)-, - CH(OH)-, -S(=O)
2-, -Si(CH
3)
2-, -C(CH
3)
2-, and -C(CF
3)
2-.
[0069] e is selected from integers of 1 to 5. When e is 2 or more, the Es may be the same
as, or different from, each other.
[0071] Specifically, (E)
e in Formula 1 may be selected from the groups represented by the following Formulae
1-1b to 1-13b, but it is not limited thereto.

[0072] More specifically, (E)
e in Formula 1 may be the group represented by the above Formula 1-6b or the group
represented by the above Formula 1-9b.
[0073] In an embodiment, the diamine compound may comprise a compound having a fluorine-containing
substituent or a compound having an ether group (-O-).
[0074] The diamine compound may be composed of a compound having a fluorine-containing substituent.
In such an event, the fluorine-containing substituent may be a fluorinated hydrocarbon
group and specifically may be a trifluoromethyl group. But it is not limited thereto.
[0075] In some embodiments, the diamine compound may comprise one kind of diamine compound.
That is, the diamine compound may be composed of a single component.
[0076] For example, the diamine compound may comprise 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl
(TFDB) represented by the following formula, but it is not limited thereto.

[0077] The dicarbonyl compound is not particularly limited, but it may be, for example,
a compound represented by the following Formula 3.

[0078] In Formula 3, J may be selected from a substituted or unsubstituted divalent C
6-C
30 aliphatic cyclic group, a substituted or unsubstituted divalent C
4-C
30 heteroaliphatic cyclic group, a substituted or unsubstituted divalent C
6-C
30 aromatic cyclic group, a substituted or unsubstituted divalent C
4-C
30 heteroaromatic cyclic group, a substituted or unsubstituted C
1-C
30 alkylene group, a substituted or unsubstituted C
2-C
30 alkenylene group, a substituted or unsubstituted C
2-C
30 alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)
2-, - Si(CH
3)
2-, -C(CH
3)
2-, and -C(CF
3)
2-.
[0079] j is selected from integers of 1 to 5. When j is 2 or more, the J groups may be the
same as, or different from, each other.
[0080] X is a halogen atom. Specifically, X may be F, Cl, Br, I, or the like. More specifically,
X may be Cl, but it is not limited thereto.
[0083] More specifically, (J)
j in Formula 3 may be the group represented by the above Formula 3-1b, the group represented
by the above Formula 3-2b, the group represented by the above Formula 3-3b, or the
group represented by the above Formula 3-8b.
[0084] In an embodiment, the dicarbonyl compound may comprise a mixture of at least two
kinds of dicarbonyl compounds different from each other. If two or more dicarbonyl
compounds are used, at least two dicarbonyl compounds in which (J)j in the above Formula
3 is selected from the groups represented by the above Formulae 3-lb to 3-8b may be
used as the dicarbonyl compound.
[0085] In another embodiment, the dicarbonyl compound may be an aromatic dicarbonyl compound
that contains an aromatic structure.
[0087] In an embodiment, the polyamide-based polymer may comprise two or more types of an
amide-based repeat unit.
[0088] For example, the two or more types of an amide-based repeat unit may comprise a first
amide-based repeat unit and a second amide-based repeat unit. The first amide-based
repeat unit may be formed by reacting a first dicarbonyl compound with the diamine
compound. The second amide-based repeat unit may be formed by reacting a second dicarbonyl
compound with the diamine compound.
[0089] The first dicarbonyl compound and the second dicarbonyl compound may be compounds
different from each other.
[0090] The first dicarbonyl compound and the second dicarbonyl compound may comprise two
carbonyl groups, respectively. The angle between the two carbonyl groups contained
in the first dicarbonyl compound may be greater than the angle between the two carbonyl
groups contained in the second dicarbonyl compound.
[0091] In some embodiments, the first dicarbonyl compound and the second dicarbonyl compound
may be structural isomers to each other. As two kinds of dicarbonyl compounds in a
structural isomeric relationship are used, a polyamide-based polymer and a film satisfying
Equation 1 and/or Equation 2 above can be formed, thereby enhancing the optical properties
and mechanical properties of the polyamide-based film.
[0092] The first dicarbonyl compound and the second dicarbonyl compound may be an aromatic
dicarbonyl compound, respectively. In some embodiments, the first dicarbonyl compound
and the second dicarbonyl compound may each have one benzene ring (a phenyl group).
[0093] For example, the first dicarbonyl compound and the second dicarbonyl compound may
be aromatic dicarbonyl compounds different from each other, but they are not limited
thereto.
[0094] If the first dicarbonyl compound and the second dicarbonyl compound are an aromatic
dicarbonyl compound, respectively, they comprise a benzene ring. Thus, they can contribute
to improvements in the mechanical properties such as surface hardness and tensile
strength of a film that comprises the polyamide-based polymer thus produced.
[0095] For example, the angle between the two carbonyl groups contained in the first dicarbonyl
compound may be 160 to 180°, and the angle between the two carbonyl groups contained
in the second dicarbonyl compound may be 80 to 140°.
[0096] For example, the dicarbonyl compound may comprise a first dicarbonyl compound and/or
a second dicarbonyl compound.
[0097] For example, the first dicarbonyl compound may comprise TPC, and the second dicarbonyl
compound may comprise IPC, but they are not limited thereto.
[0098] If TPC is used as the first dicarbonyl compound and IPC is used as the second dicarbonyl
compound in a proper combination, a film that comprises the polyamide-based resin
thus produced may have high light transmittance, low haze, high transparency, and
high modulus with enhanced light resistance.
[0099] The diamine compound and the dicarbonyl compound may be polymerized to form a repeat
unit represented by the following Formula B.

[0100] In Formula B, E, J, e, and j are as described above.
[0101] For example, the diamine compound and the dicarbonyl compound may be polymerized
to form amide repeat units represented by the following Formulae B-1 and B-2.

[0102] In Formula B-1, y is an integer of 1 to 400.

[0103] In Formula B-2, y is an integer of 1 to 400.
[0104] In some embodiments, the molar ratio of the first amide-based repeat unit to the
second amide-based repeat unit may be 21:79 to 79:21. As the molar ratio of the first
and second amide-based repeat units is set to the above range, the light resistance
index and/or light resistance color change index of the polyamide-based film may be
adjusted to ranges satisfying Equations 1 and 2 above. Thus, the mechanical and optical
properties and the light resistance of the polyamide-based film may be improved. Preferably,
the molar ratio of the first amide-based repeat unit to the second amide-based repeat
unit may be 25:75 to 75:25, 30:70 to 75:25, 30:70 to 70:30, 35:65 to 75:25, or 40:60
to 75:25.
[0105] The dianhydride compound is not particularly limited, but it may comprise a cyclic
dianhydride compound. For example, the dianhydride compound may reduce the birefringence
characteristics of the polyamide-based resin and enhance such optical properties as
transmittance of the polyamide-based film.
[0106] In some embodiments, the cyclic dianhydride compound may comprise an alicyclic dianhydride
compound or an aromatic dianhydride compound.
[0107] The alicyclic dianhydride compound may comprise a compound in which two anhydride
groups are substituted in the alicyclic ring structure. The alicyclic ring structure
may contain 4 to 12 carbons and may be fully saturated or partially unsaturated. Specifically,
the alicyclic dianhydride compound may comprise, for example, 1,2,3,4-cyclobutanetetracarboxylic
dianhydride (CBDA).
[0108] The aromatic dianhydride compound may comprise a compound in which two anhydride
groups are substituted in an aromatic ring having 6 to 30 carbon atoms. The aromatic
ring may comprise benzene, a fused ring such as naphthalene, or a linked ring such
as biphenyl. For example, the aromatic dianhydride compound may comprise, for example,
3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA).
[0109] The two anhydride groups in the dianhydride compound may be directly substituted
to the cyclic hydrocarbon group or may be substituted at positions symmetrical to
each other in the alicyclic ring or the aromatic ring. In such a case, the hardness
and restoring force to indentation of the polyamide-based film may be enhanced.
[0110] In an embodiment, the dianhydride compound may not comprise a fluorine-containing
substituent. For example, when the dianhydride compound contains a fluorine group,
the plastic component of the film may be excessively increased; thus, its flexibility
and restoring force to indentation may be reduced.
[0111] For example, the dianhydride compound may comprise a compound represented by the
following Formula 2.

[0112] In Formula 2, G is a substituted or unsubstituted tetravalent C
4-C
12 aliphatic cyclic group, a substituted or unsubstituted tetravalent C
4-C
12 heteroaliphatic cyclic group, a substituted or unsubstituted tetravalent C
6-C
30 aromatic cyclic group, or a substituted or unsubstituted tetravalent C
4-C
30 heteroaromatic cyclic group, wherein the aliphatic cyclic group, the heteroaliphatic
cyclic group, the aromatic cyclic group, or the heteroaromatic cyclic group may be
present alone, fused to each other to form a condensed ring, or bonded by a bonding
group selected from -O-, -S-, -C(=O)-, and -S(=O)
2-.
[0114] For example, G in Formula 2 may be the group represented by the above Formula 2-2a,
the group represented by the above Formula 2-8a, or the group represented by the above
Formula 2-9a.
[0115] For example, the dianhydride compound may comprise 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane
dianhydride (6-FDA) represented by the following formula, but it is not limited thereto.

[0116] The diamine compound and the dianhydride compound may be polymerized to form an amic
acid group.
[0117] Subsequently, the amic acid group may be converted to an imide group through a dehydration
reaction. In such a case, a polyamide-imide-based polymer comprising a polyimide segment
and a polyamide segment may be formed.
[0118] The polyimide segment may form a repeat unit represented by the following Formula
A.

[0119] In Formula A, E, G, and e are as described above.
[0120] For example, the polyimide segment may comprise a repeat unit represented by the
following Formula A-1, but it is not limited thereto.

[0121] In Formula A-1, n may be an integer of 1 to 400.
[0122] In some embodiments, the polyamide-based polymer may comprise an amide-based repeat
unit and an imide-based repeat unit at a molar ratio of 100:0 to 90:0. In such a case,
mechanical properties such as flexibility and mechanical strength and optical properties
such as transparency, transmittance, and haze of the polyamide-based film may be improved
together.
[0123] Preferably, the polyamide-based polymer may not comprise an imide-based repeat unit.
In such a case, the light resistance index and/or the light resistance color change
index can be effectively adjusted to the above ranges. As a result, the light resistance
of the polyamide-based film may be enhanced.
[0124] In some embodiments, the polyamide-based film may comprise a blue pigment. The blue
pigment may comprise OP-1300A manufactured by Toyo, but it is not limited thereto.
[0125] In some embodiments, the blue pigment may be employed in an amount of 50 to 5,000
ppm based on the total weight of the polyamide-based polymer. In such a case, the
yellow index before and after the light resistance test of the film may be decreased.
Preferably, the blue pigment may be employed in an amount of 100 to 5,000 ppm, 200
to 5,000 ppm, 300 to 5,000 ppm, 400 to 5,000 ppm, 50 to 3,000 ppm, 100 to 3,000 ppm,
200 to 3,000 ppm, 300 to 3,000 ppm, 400 to 3,000 ppm, 50 to 2,000 ppm, 100 to 2,000
ppm, 200 to 2,000 ppm, 300 to 2,000 ppm, 400 to 2,000 ppm, 50 to 1,000 ppm, 100 to
1,000 ppm, 200 to 1,000 ppm, 300 to 1,000 ppm, or 400 to 1,000 ppm, based on the total
weight of the polyamide-based polymer.
[0126] In some embodiments, the polyamide-based film may further comprise a UVA absorber.
The UVA absorber may comprise an absorber that absorbs electromagnetic waves of a
wavelength of 10 to 400 nm used in the art. For example, the UVA absorber may comprise
a benzotriazole-based compound. The benzotriazole-based compound may comprise an N-phenolic
benzotriazole-based compound. In some embodiments, the N-phenolic benzotriazole-based
compound may comprise N-phenolic benzotriazole in which the phenol group is substituted
with an alkyl group having 1 to 10 carbon atoms. It may be substituted with two or
more of the alkyl group, which may be linear, branched, or cyclic.
[0127] In some embodiments, the UVA absorber may be employed in an amount of 0.1 to 10%
by weight based on the total weight of the polyamide-based polymer. In such a case,
the light resistance of the film can be enhanced. Preferably, the UVA absorber may
be employed in an amount of 0.1 to 5% by weight, 0.1 to 3% by weight, 0.1 to 2% by
weight, 0.5 to 10% by weight, 0.5 to 5% by weight, 0.5 to 3% by weight, 0.5 to 2%
by weight, 1 to 10% by weight, 1 to 5% by weight, 1 to 3% by weight, or 1 to 2% by
weight, relative to the total weight of the polyamide-based polymer.
[0128] In some embodiments, the polyamide-based film may comprise a blue pigment and a UVA
absorber together. In such a case, the yellow index of the film may be reduced, the
transparency thereof may be enhanced, and the rate of increase in yellow index and
the color difference upon the light resistance test may be reduced.
[0129] In some embodiments, the polyamide-based film may have a thickness deviation of 4
µm or less based on a thickness of 50 µm. The thickness deviation may refer to a deviation
between the maximum or minimum value with respect to the average of thicknesses measured
at 10 random points of the film. In such a case, as the polyamide-based film has a
uniform thickness, its optical properties and mechanical properties at each point
may be uniformly exhibited.
[0130] The polyamide-based film may have a haze of 1% or less. For example, the haze may
be 0.7% or less or 0.5% or less, but it is not limited thereto. The haze may be measured
using a haze meter, for example a NDH-5000W manufactured by Nippon Denshoku Kogyo,
in accordance with the JIS K 7136 standard.
[0131] The polyamide-based film may have a transmittance of 80% or more. For example, the
transmittance may be 82% or more, 85% or more, 88% or more, 89% or more, 80% to 99%,
88% to 99%, or 89% to 99%, but it is not limited thereto. The light transmittance
may be measured using a haze meter, for example a NDH-5000W manufactured by Nippon
Denshoku Kogyo, in accordance with the JIS K 7136 standard.
[0132] The polyamide-based film may have a yellow index of 3 or less. For example, the yellow
index may be 2.8 or less or 2.5 or less, but it is not limited thereto. The yellow
index (YI) may be measured with a spectrophotometer, for example, an UltraScan PRO,
Hunter Associates Laboratory, under the conditions of d65 and 10° in accordance with
the ASTM-E313 standard.
[0133] The polyamide-based film may have a modulus (Y) of 4 GPa or more. Specifically, the
modulus may be 5 GPa or more, 6 GPa or more, 6.3 GPa or more, or 6.5 GPa or more,
but it is not limited thereto. The modulus may be measured using a universal testing
machine, such as a UTM 5566A of Instron. In an exemplary method of measuring the modulus,
a sample is cut out by at least 10 cm in the direction perpendicular to the main shrinkage
direction of the film and by 10 cm in the main shrinkage direction and then fixed
by clips disposed at an interval of 10 cm in a universal testing machine UTM 5566A
of Instron. A stress-strain curve is then obtained until the sample is fractured while
it is stretched at a speed of 12.5 mm/minute at room temperature. The slope of the
load with respect to the initial strain on the stress-strain curve is taken as the
modulus (GPa).
[0134] The polyamide-based film may have a compressive strength of 0.4 kgf/µm or more. Specifically,
the compressive strength may be 0.45 kgf/µm or more, or 0.46 kgf/µm or more, but it
is not limited thereto.
[0135] When the polyamide-based film is perforated at a speed of 10 mm/min using a 2.5-mm
spherical tip in a UTM compression mode, the maximum diameter (mm) of perforation
including a crack is 60 mm or less. Specifically, the maximum diameter of perforation
may be 5 to 60 mm, 10 to 60 mm, 15 to 60 mm, 20 to 60 mm, 25 to 60 mm, or 25 to 58
mm, but it is not limited thereto.
[0136] The polyamide-based film may have a surface hardness of HB or higher. Specifically,
the surface hardness may be H or higher, or 2H or higher, but it is not limited thereto.
[0137] The polyamide-based film may have a tensile strength of 15 kgf/mm
2 or more. Specifically, the tensile strength may be 18 kgf/mm
2 or more, 20 kgf/mm
2 or more, 21 kgf/mm
2 or more, or 22 kgf/mm
2 or more, but it is not limited thereto.
[0138] The polyamide-based film may have an elongation of 15% or more. Specifically, the
elongation may be 16% or more, 17% or more, or 17.5% or more, but it is not limited
thereto.
[0139] The polyamide-based film according to an embodiment may be enhanced in flexibility
and transparency and suppressed in a change in transparency and color due to UV rays.
[0140] The physical properties of the polyamide-based film as described above are based
on a thickness of 40 µm to 60 µm. For example, the physical properties of the polyamide-based
film are based on a thickness of 50 µm.
[0141] The features on the components and properties of the polyamide-based film as described
above may be combined with each other.
[0142] For example, the polyamide-based film comprises a polyamide-based polymer and may
have a transmittance of 80% or more, a haze of 1% or less, and a yellow index of 3
or less.
[0143] In addition, the light resistance index and the light resistance color change index
of the polyamide-based film as described above may be adjusted by combinations of
the chemical and physical properties of the components, which constitute the polyamide-based
film, along with the conditions in each step of the process for preparing the polyamide-based
film as described below.
[0144] For example, the compositions and contents of the components that constitute the
polyamide-based film, the polymerization conditions and thermal treatment conditions
in the film preparation process, and the like are all combined to achieve the light
resistance index and/or the light resistance color change index in desired ranges.
Cover window for a display device
[0145] The cover window for a display device according to an embodiment comprises a polyamide-based
film and a functional layer.
[0146] The polyamide-based film comprises a polyamide-based polymer, wherein the light resistance
index represented by the above Equation 1 is 0.660 GPa
-1 or less.
[0147] Details on the polyamide-based film are as described above.
[0148] The cover window for a display device can be advantageously applied to a display
device.
[0149] As the polyamide-based film has a light resistance index within the above range,
it may have excellent optical and mechanical properties, and its light resistance
to UV rays may be enhanced.
Display device
[0150] The display device according to an embodiment comprises a display unit; and a cover
window disposed on the display unit, wherein the cover window comprises a polyamide-based
film and a functional layer.
[0151] The polyamide-based film comprises a polyamide-based polymer, wherein the light resistance
index represented by the above Equation 1 is 0.660 GPa
-1 or less.
[0152] Details on the polyamide-based film and the cover window are as described above.
Fig. 1 is a schematic exploded view of a display device according to an embodiment.
Fig. 2 is a schematic perspective view of a display device according to an embodiment.
Fig. 3 is a schematic cross-sectional view of a display device according to an embodiment.
[0153] Specifically, Figs. 1 to 3 illustrate a display device, which comprises a display
unit (400) and a cover window (300) disposed on the display unit (400), wherein the
cover window comprises a polyamide-based film (100) having a first side (101) and
a second side (102) and a functional layer (200), and an adhesive layer (500) is interposed
between the display unit (400) and the cover window (300).
[0154] The display unit (400) is for displaying an image, and it may have flexible characteristics.
[0155] The display unit (400) may be a display panel for displaying an image. For example,
it may be a liquid crystal display panel or an organic electroluminescent display
panel. The organic electroluminescent display panel may comprise a front polarizing
plate and an organic EL panel.
[0156] The front polarizing plate may be disposed on the front side of the organic EL panel.
Specifically, the front polarizing plate may be attached to the side on which an image
is displayed in the organic EL panel.
[0157] The organic EL panel may display an image by self-emission of a pixel unit. The organic
EL panel may comprise an organic EL substrate and a driving substrate. The organic
EL substrate may comprise a plurality of organic electroluminescent units, each of
which corresponds to a pixel. Specifically, it may comprise a cathode, an electron
transport layer, a light-emitting layer, a hole transport layer, and an anode. The
driving substrate is operatively coupled to the organic EL substrate. That is, the
driving substrate may be coupled to the organic EL substrate so as to apply a driving
signal such as a driving current, so that the driving substrate can drive the organic
EL substrate by applying a current to the respective organic electroluminescent units.
[0158] In addition, an adhesive layer (500) may be interposed between the display unit (400)
and the cover window (300). The adhesive layer may be an optically transparent adhesive
layer, but it is not particularly limited.
[0159] The cover window (300) may be disposed on the display unit (400). The cover window
is located at the outer position of the display device to thereby protect the display
unit.
[0160] The cover window (300) may comprise a polyamide-based film and a functional layer.
The functional layer may be at least one selected from the group consisting of a hard
coating layer, a reflectance reducing layer, an antifouling layer, and an antiglare
layer. The functional layer may be coated on at least one side of the polyamide-based
film.
[0161] The polyamide-based film according to an embodiment can be applied in the form of
a film to the outside of a display device without changing the display driving method,
the color filter inside the panel, or the laminated structure, thereby providing a
display device having a uniform thickness, low haze, high transmittance, and high
transparency. Since neither significant process changes nor cost increases are needed,
it is advantageous in that the production costs can be reduced.
[0162] The polyamide-based film according to an embodiment may be excellent in optical properties
in terms of high transmittance, low haze, and low yellow index, as well as may have
excellent mechanical properties such as modulus and flexibility, and the change (deterioration)
of its optical and mechanical properties can be suppressed when it is exposed to UV
rays
[0163] Specifically, the polyamide-based film having a light resistance index and/or a light
resistance color change index in the above ranges has excellent transparency, flexibility,
and light resistance. Thus, its transparency and flexibility can be maintained for
a long period of time even in an environment that can be strongly exposed to ultraviolet
rays such as outdoors. Accordingly, it can be advantageously applied to an outdoor
flexible display device, a portable flexible displace device, or the like.
Process for preparing a polyamide-based film
[0164] An embodiment provides a process for preparing a polyamide-based film.
[0165] The process for preparing a polyamide-based film according to an embodiment comprises
polymerizing a diamine compound and a dicarbonyl compound to prepare a solution comprising
a polyamide-based polymer in an organic solvent; casting the solution and then drying
it to prepare a gel sheet; and thermally treating the gel sheet.
[0166] Referring to Fig. 4, the process for preparing a polyamide-based film according to
an embodiment comprises polymerizing a diamine compound and a dicarbonyl compound
in an organic solvent to prepare a solution comprising a polyamide-based polymer (S100);
casting the polymer solution to prepare a gel sheet (S200); and thermally treating
the gel sheet (S300).
[0167] The process for preparing a polyamide-based film according to some embodiments may
further comprise adjusting the viscosity of the polyamide-based polymer solution (S110),
aging the polyamide-based polymer solution (S120), and/or degassing the polyamide-based
polymer solution (S130).
[0168] The polyamide-based film is a film in which a polyamide-based polymer is a main component.
The polyamide-based polymer is a resin that comprises an amide repeat unit as a structural
unit. Optionally, the polyamide-based polymer may comprise an imide repeat unit.
[0169] In the process for preparing a polyamide-based film, the polymer solution for preparing
a polyamide-based polymer may be prepared by simultaneously or sequentially mixing
a diamine compound and a dicarbonyl compound in an organic solvent in a reactor, and
reacting the mixture (S 100).
[0170] In an embodiment, the step of preparing the polymer solution may comprise mixing
and reacting the diamine compound and the dicarbonyl compound in a solvent to produce
a polyamide (PA) solution. The polyamide solution is a solution that comprises a polymer
having an amide repeat unit.
[0171] In an embodiment, the step of preparing the polymer solution may be carried out by
using two kinds of dicarbonyl compounds different from each other as the dicarbonyl
compound. In such a case, the two kinds of dicarbonyl compounds may be mixed and reacted
simultaneously or sequentially. Preferably, the first dicarbonyl compound and the
diamine compound may react to form a prepolymer, and the prepolymer and the second
dicarbonyl compound may react to form the polyamide-based polymer. In such a case,
the light resistance index and/or the light resistance color change index of the polyamide-based
polymer may be readily adjusted.
[0172] Details on the diamine compound and the dicarbonyl compound are as described above.
[0173] In an embodiment, the process may further comprise adjusting the viscosity of the
polymer solution (S110) after the step of preparing the polymer solution. The viscosity
of the polymer solution may be 200,000 cps to 350,000 cps at room temperature. In
such an event, the film-forming capability of a polyamide-based film can be enhanced,
thereby enhancing the thickness uniformity.
[0174] Specifically, the step of preparing the polymer solution may comprise simultaneously
or sequentially mixing and reacting a diamine compound and a dicarbonyl compound in
an organic solvent to prepare a first polymer solution; and further adding the dicarbonyl
compound to prepare a second polymer solution having the target viscosity.
[0175] In the steps of preparing the first polymer solution and the second polymer solution,
the stirring speeds may be different from each other. For example, the stirring speed
when the first polymer solution is prepared may be faster than the stirring speed
when the second polymer solution is prepared.
[0176] In some embodiments, when the first polymer solution is prepared, the first dicarbonyl
compound and the second dicarbonyl compound may be sequentially reacted with the diamine
compound. In such an event, a first polymer solution having a viscosity of 1,000 to
10,000 cps may be formed. Preferably, the viscosity of the first polymer solution
may be 1,000 to 8,000 cps, 1,000 to 5,000 cps, 2,000 to 10,000 cps, 2,000 to 8,000
cps, 2,000 to 5,000 cps, 3,000 to 10,000 cps, 3,000 to 8,000 cps, or 3,000 to 5,000
cps.
[0177] In some embodiments, the second dicarbonyl compound may be further reacted with the
first polymer solution to form a second polymer solution having a viscosity of 200,000
to 350,000 cps. For example, the step of further reacting the second dicarbonyl compound
may serve as the step of viscosity adjustment.
[0178] As the viscosity of the polyamide-based polymer solution is adjusted through the
first polymer solution and the second polymer solution, the light resistance index
and the light resistance color change index in desired ranges can be effectively achieved.
[0179] For example, the viscosity of the polymer solution, light resistance index, and light
resistance color change index may be adjusted by controlling the sequence and amounts
of the first dicarbonyl compound and the second dicarbonyl compound added.
[0180] The molar ratio of the first dicarbonyl compound to the second dicarbonyl compound
for the preparation of the polymer solution may be 21:79 to 79:21, preferably, 25:75
to 75:25, 30:70 to 75:25, 30:70 to 70:30, 35:65 to 75:25, or 40:60 to 75:25.
[0181] As the first dicarbonyl compound and the second dicarbonyl compound are used at such
a ratio, it is possible to prepare a polyamide-based polymer having a light resistance
index and/or a light resistance color change index within the above ranges and to
improve the modulus, haze, transmittance, yellow index, light resistance, and the
like of the polyamide-based film.
[0182] In some embodiments, when the polymer solution (first polymer solution) is formed,
a dianhydride compound is reacted with a diamine compound to form a polyamic acid
or a polyimide. Then, the polyamic acid or polyimide may be reacted with a dicarbonyl
compound to form a polymer solution comprising a polyamide-imide. In such an event,
the dianhydride compound as described above may be used. Its amount used may be 1
to 10% by mole, 1 to 3% by mole, or 1 to 5% by mole, based on the total amount of
the dicarbonyl compound and the dianhydride compound. In such a case, the viscosities
of the polymer solution, the first polymer solution, and the second polymer solution
can be adjusted to desired ranges, and a polyamide-based film having a light resistance
index and/or a light resistance color change index in the desired ranges can be prepared.
In some embodiments, the dianhydride compound may not be used in the formation of
the polymer solution. In such a case, a polyamide-based polymer that does not comprise
the imide repeat unit may be formed.
[0183] In an embodiment, the mixing and reaction of the solvent, the diamine compound, and
the dicarbonyl compound may be carried out at a temperature of -20 to 25°C. If it
is outside the above temperature range, excessively few or many polymerization nuclei
are formed, thereby making it difficult to form a polyamide-based polymer having a
light resistance index and a light resistance color change index in the desired ranges.
Thus, the mechanical properties and optical properties of the polyamide-based film
may be deteriorated. In addition, the viscosity of the polymer solution may be less
than a predetermined range. Preferably, the reaction of the diamine compound and the
dicarbonyl compound may be carried out at a temperature of -20 to 20°C, -20 to 15°C,
-20 to 10°C, - 15 to 20°C, -15 to 15°C, -15 to 10°C, -10 to 20°C, -10 to 15°C, -10
to 10°C, -8 to 20°C, -8 to 15°C, -8 to 10°C, -5 to 20°C, -5 to 15°C, or -5 to 10°C.
[0184] In an embodiment, the mixing and reaction of the diamine compound and the dianhydride
compound may be carried out at a temperature of 0 to 50°C. If it is outside the above
temperature range, excessively few or many polymerization nuclei are formed, thereby
making it difficult to form a polyamide-based polymer having a light resistance index
and a light resistance color change index in the desired ranges. Thus, the mechanical
properties and optical properties of the polyamide-based film may be deteriorated.
In addition, the viscosity of the polymer solution may be less than a predetermined
range. Preferably, the mixing and reaction of the diamine compound and the dianhydride
compound may be carried out at a temperature of 0 to 45°C, 0 to 40°C, 10 to 50°C,
10 to 45°C, 10 to 40°C, 20 to 50°C, 20 to 45°C, or 20 to 40°C.
[0185] The content of solids contained in the polymer solution may be 10% by weight to 30%
by weight, but it is not limited thereto.
[0186] If the content of solids contained in the polymer solution is within the above range,
a polyamide-based film can be effectively produced in the casting step. In addition,
the polyamide-based film thus produced may have enhanced mechanical properties and
optical properties.
[0187] In still another embodiment, the step of preparing the polymer solution may further
comprise adjusting the pH of the polymer solution. In this step, the pH of the polymer
solution may be adjusted to 4 to 7, for example, 4.5 to 7.
[0188] The pH of the polymer solution may be adjusted by adding a pH adjusting agent. The
pH adjusting agent is not particularly limited and may include, for example, amine-based
compounds such as alkoxyamine, alkylamine, and alkanolamine.
[0189] As the pH of the polymer solution is adjusted to the above range, it is possible
to prevent the occurrence of defects in the film produced from the polymer solution
and to achieve the desired optical properties and mechanical properties in terms of
yellow index and modulus.
[0190] The pH adjusting agent may be employed in an amount of 0.1% by mole to 10% by mole
based on the total number of moles of monomers in the polymer solution.
[0191] In an embodiment, the organic solvent may be at least one selected from the group
consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone
(NMP), m-cresol, tetrahydrofuran (THF), and chloroform. The organic solvent employed
in the polymer solution may be dimethylacetamide (DMAc), but it is not limited thereto.
[0192] In some embodiments, at least one of a blue pigment and a UVA absorber may be added
to the polymer solution. The types and contents of the blue pigment and the UVA absorber
are as described above. The blue pigment and the UVA absorber may be mixed with the
polyamide-based polymer in the polymer solution.
[0193] The polymer solution may be stored at -20°C to 20°C, -20°C to 10°C, -20°C to 5°C,
-20°C to 0°C, or 0°C to 10°C.
[0194] If it is stored at the above temperature, it is possible to prevent degradation of
the polymer solution and to lower the moisture content to thereby prevent defects
of a film produced therefrom.
[0195] In some embodiments, the polymer solution or the polymer solution whose viscosity
has been adjusted may be aged (S 120).
[0196] The aging may be carried out by leaving the polymer solution at a temperature of
- 10 to 10°C for 24 hours or longer. In such an event, the polyamide-based polymer
or unreacted materials contained in the polymer solution, for example, may complete
the reaction or achieve chemical equilibrium, whereby the polymer solution may be
homogenized. The mechanical properties and optical properties of a polyamide-based
film formed therefrom may be substantially uniform over the entire area of the film.
Preferably, the aging may be carried out at a temperature of -5 to 10°C, -5 to 5°C,
or -3 to 5°C.
[0197] In an embodiment, the process may further comprise degassing the polyamide-based
polymer solution (S130). The step of degassing may remove moisture in the polymer
solution and reduce impurities, thereby increasing the reaction yield and imparting
excellent surface appearance and mechanical properties to the film finally produced.
[0198] The degassing may comprise vacuum degassing or purging with an inert gas.
[0199] The vacuum degassing may be carried out for 30 minutes to 3 hours after depressurizing
the internal pressure of the tank in which the polymer solution is contained to 0.1
bar to 0.7 bar. The vacuum degassing under these conditions may reduce bubbles in
the polymer solution. As a result, it is possible to prevent surface defects of the
film produced therefrom and to achieve excellent optical properties such as haze.
[0200] Specifically, the purging may be carried out by purging the tank with an inert gas
at an internal pressure of 1 atm to 2 atm. The purging under these conditions may
remove moisture in the polymer solution, reduce impurities to thereby increase the
reaction yield, and achieve excellent optical properties such as haze and mechanical
properties.
[0201] The inert gas may be at least one selected from the group consisting of nitrogen,
helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), but
it is not limited thereto. Specifically, the inert gas may be nitrogen.
[0202] The vacuum degassing and the purging with an inert gas may be carried out in separate
steps.
[0203] For example, the step of vacuum degassing may be carried out, followed by the step
of purging with an inert gas, but it is not limited thereto.
[0204] The vacuum degassing and/or the purging with an inert gas may improve the physical
properties of the surface of a polyamide-based film thus produced.
[0205] Once the solution comprising a polyamide-based polymer in an organic solvent has
been prepared as described above, a filler may be added to the solution.
[0206] The filler has an average particle diameter of 60 nm to 180 nm and a refractive index
of 1.55 to 1.75. The content thereof is 100 ppm to 3,000 ppm based on the total weight
of the solids content of the polyamide-based polymer. Details on the filler are as
described above.
[0207] The polymer solution may be cast to prepare a gel sheet (S200).
[0208] For example, the polymer solution may be extruded, coated, and/or dried on a support
to form a gel sheet.
[0209] In addition, the casting thickness of the polymer solution may be 200 µm to 700 µm.
As the polymer solution is cast to a thickness within the above range, the final film
produced after the drying and thermal treatment may have an appropriate and uniform
thickness.
[0210] The polymer solution may have a viscosity of 200,000 cps to 350,000 cps at room temperature
as described above. As the viscosity satisfies the above range, the polymer solution
can be cast to a uniform thickness without defects, and a polyamide-based film having
a substantially uniform thickness can be formed without local/partial thickness variations
during drying. In addition, a film having a light resistance index and/or a light
resistance color change index as described above can be produced.
[0211] The polymer solution thus cast is then dried at a temperature of 60°C to 150°C for
5 minutes to 60 minutes to prepare a gel sheet. Specifically, the polymer solution
is dried at a temperature of 70°C to 90°C for 15 minutes to 40 minutes to prepare
a gel sheet.
[0212] The solvent of the polymer solution may be partially or totally volatilized during
the drying to prepare the gel sheet.
[0213] The dried gel sheet may be thermally treated to form a polyamide-based film (S300).
[0214] The thermal treatment of the gel sheet may be carried out, for example, through a
thermosetting device.
[0215] The thermosetting device may thermally treat the gel sheet through hot air.
[0216] If the thermal treatment is carried out with hot air, the heat may be uniformly supplied.
If the heat is not uniformly supplied, a satisfactory surface roughness cannot be
achieved, which may raise or lower the surface energy too much.
[0217] The thermal treatment of the gel sheet may be carried out in a temperature range
of 60°C to 500°C for 5 minutes to 200 minutes. Specifically, the thermal treatment
of the gel sheet may be carried out in a temperature range of 80°C to 300°C at a temperature
elevation rate of 1.5°C/minute to 20°C/minute for 10 minutes to 150 minutes.
[0218] In such an event, the initial temperature of the thermal treatment of the gel sheet
may be 60°C or higher. Specifically, the initial temperature of the thermal treatment
of the gel sheet may be 80°C to 180°C.
[0219] In addition, the maximum temperature in the thermal treatment may be 300°C to 500°C.
For example, the maximum temperature in the thermal treatment may be 350°C to 500°C,
380°C to 500°C, 400°C to 500°C, 410°C to 480°C, 410°C to 470°C, or 410°C to 450°C.
[0220] According to an embodiment, the thermal treatment of the gel sheet may be carried
out in two or more steps.
[0221] Specifically, the thermal treatment may comprise a first hot air treatment step carried
out for 5 minutes to 30 minutes in a range of 60°C to 120°C; and a second hot air
treatment step carried out for 10 minutes to 120 minutes in a range of 120°C to 350°C.
[0222] The thermal treatment under these conditions may cure the gel sheet to have appropriate
surface hardness, modulus, and surface energy and may secure high light transmittance,
low haze, and an appropriate level of glossiness of the cured film at the same time.
[0223] According to an embodiment, the thermal treatment may comprise passing it through
an IR heater. The thermal treatment by an IR heater may be carried out for 1 minute
to 30 minutes in a temperature range of 300°C or higher. Specifically, the thermal
treatment by an IR heater may be carried out for 1 minute to 20 minutes in a temperature
range of 300°C to 500°C.
[0224] The polyamide-based film is prepared by the preparation process as described above
such that it may have a light resistance index and a light resistance color change
index as described above and may be excellent in optical properties, mechanical properties,
and light resistance.
[0225] The polyamide-based film can be applied to various uses that require flexibility,
transparency, and a certain level of luminance. For example, the polyamide-based film
can be applied to solar cells, displays, semiconductor devices, sensors, and the like.
[0226] In particular, since the polyamide-based film has excellent mechanical and optical
properties and light resistance, it can be advantageously applied to a cover window
for a display device and to a display device. Since it has excellent folding characteristics,
it can be advantageously applied to a foldable display device or a flexible display
device.
[0227] Details on the polyamide-based film prepared by the process for preparing a polyamide-based
film are as described above.
Embodiments for Carrying Out the Invention
[0228] Hereinafter, the present invention will be described in more detail with reference
to the following examples. However, these examples are set forth to illustrate the
present invention, and the scope of the present invention is not limited thereto.
<Example 1>
[0229] A 1-liter glass reactor equipped with a temperature-controllable double jacket was
charged with 567 g of dimethylacetamide (DMAc) as an organic solvent at 10°C under
a nitrogen atmosphere. Then, 64.0 g (0.200 mole) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl
(TFMB) as an aromatic diamine was slowly added thereto and dissolved.
[0230] Subsequently, 30.37 g (0.15 mole) of terephthaloyl chloride (TPC) was slowly added
while the mixture was stirred for 1 hour. Then, 9.13 g (0.05 mole; 94% by mole of
the total amount introduced) of isophthaloyl chloride (IPC) was added, followed by
stirring the mixture for 1 hour, thereby preparing a first polymer solution. The viscosity
of the first polymer solution was about 1,000 to 10,000 cps.
[0231] Then, 1 ml of an IPC solution having a concentration of 10% by weight in a DMAc solvent
was added to the first polymer solution, followed by stirring the mixture for 30 minutes.
This procedure was repeated, whereby a second polymer solution having a viscosity
of about 250,000 cps was prepared. Here, about 12.18 g of the IPC solution was added.
The amount of IPC added corresponded to the balanced amount of the number of moles
of TPC and IPC added relative to the total number of moles of TFMB in the preparation
of the first polymer solution.
[0232] The second polymer solution was coated onto a glass plate and then dried with hot
air at 100°C for 30 minutes. The dried polyamide polymer material was peeled off from
the glass plate, fixed to a pin frame, and thermally treated in a temperature range
of 80°C to 300°C at a temperature elevation rate of 2°C/minute to obtain a polyamide
film having a thickness of 50 µm.
<Examples 2 to 5 and Comparative Example>
[0233] A polyamide film was prepared in the same manner as in Example 1, except that the
content of the dicarbonyl compound was changed as shown in Tables 1 and 2 below.
[0234] In Comparative Examples 4 to 7, before TPC was added, BPDA and 6-FDA were added and
reacted with TFMB. After BPDA and 6-FDA were reacted with TFMB at about 30°C, the
reactor temperature was lowered to 10°C, and TPC was added.
[0235] In Examples 4 and 5 and Comparative Examples 5 and 7, a blue pigment (OP-1300A manufactured
by Toyo Inc.) and/or a UVA absorber (Tinuvin 328 manufactured by BASF) were added
to the second polymer solution. The blue pigment was added at 500 ppm, and the UVA
absorber was added at 1.25% by weight, based on the total weight of the second polymer
solution.
<Evaluation Example>
[0236] The films prepared in the Examples and Comparative Examples were each measured and
evaluated for the following properties. The results are shown in Table 1 below.
Evaluation Example 1: Measurement of modulus
[0237] A sample was cut out by at least 10 cm in the direction perpendicular to the main
shrinkage direction of the film and by 10 cm in the main shrinkage direction. It was
fixed by the clips disposed at an interval of 10 cm in a universal testing machine
UTM 5566A of Instron. A stress-strain curve was obtained until the sample was fractured
while it was stretched at a speed of 12.5 mm/minute at room temperature. The slope
of the load with respect to the initial strain on the stress-strain curve was taken
as the modulus (GPa).
Evaluation Example 2: Measurement of transmittance and haze
[0238] The light transmittance and haze were measured using a haze meter NDH-5000W manufactured
by Nippon Denshoku Kogyo in accordance with the JIS K 7136 standard.
Evaluation Example 3: Measurement of yellow index
[0239] The yellow index (YI) was measured with a spectrophotometer (UltraScan PRO, Hunter
Associates Laboratory) under the conditions of d65 and 10° in accordance with the
ASTM-E313 standard.
Evaluation Example 4: Measurement of color index
[0240] The color index of the film was measured according to the CIE Lab color coordinates
using UltraScan Pro of HunterLab.
Evaluation Example 5: Evaluation of light resistance
[0241] The light resistance test cycle according to the following conditions was repeated
12 times using an Accelerated Weathering Tester (QUV/Spray, manufactured by Q-Lab).
The yellow index and color index were measured again after the light resistance test.
ΔYI, ΔE, ΔYI/Y, and ΔYI/ΔE were calculated and shown in Tables 1 and 2 below (Y: modulus).
Here, ΔE was calculated according to the following Equation 3.
[0242] Light resistance test cycle: light having a wavelength of 340 nm was irradiated to
a film sample at an intensity of 0.63 W/m
2 for 4 hours at 60°C. Then, the UV irradiation was stopped, and it was left at 50°C
for 4 hours while water was being sprayed thereto.

[0243] In Equation 3, L
∗, a
∗, and b
∗ are L, a, and b values according to the CIE Lab color coordinates after the light
resistance test, respectively, and L
∗0, a
∗0, and b
∗0 are L, a, and b values according to the CIE Lab color coordinates before the light
resistance test, respectively.
[Table 1]
|
Ex. 1 |
Ex. 2 |
Ex. 3 |
Ex. 4 |
Ex. 5 |
Polymerization ratio of polyamide-based polymer |
Diamine compound (molar ratio) |
TFMB 100 |
TFMB 100 |
TFMB 100 |
TFMB 100 |
TFMB 100 |
Dicarbonyl compound (molar ratio) |
TPC 75 |
TPC 70 |
TPC 60 |
IPC 25 |
IPC 30 |
IPC 40 |
Dianhydride compound (molar ratio) |
- |
Additive (content) |
- |
OP-1300A 500 ppm |
OP-1300A 500 ppm, Tinuvin 328 1.25 wt% |
Modulus (Y) (GPa) |
6.8 |
6.94 |
6.29 |
6.21 |
6.23 |
Transmittance (%) |
88.9 |
89.0 |
89.0 |
88.6 |
89.2 |
Hz |
0.4 |
0.4 |
0.3 |
0.6 |
0.3 |
Before light resistance test |
YI0 |
2.78 |
2.72 |
2.45 |
1.07 |
1.62 |
L∗ |
95.20 |
95.27 |
95.34 |
95.14 |
95.15 |
a∗ |
-0.15 |
-0.11 |
-0.11 |
-0.28 |
-0.45 |
b∗ |
1.52 |
1.47 |
1.33 |
0.68 |
1.04 |
After light resistance test |
YI |
6.23 |
6.12 |
5.79 |
4.93 |
4.11 |
L∗ |
95.52 |
95.57 |
95.67 |
95.33 |
95.32 |
a∗ |
-0.67 |
-0.69 |
-0.68 |
-0.90 |
-0.85 |
b∗ |
3.58 |
3.53 |
3.35 |
2.97 |
2.52 |
ΔYI (YI - YI0) |
3.45 |
3.40 |
3.34 |
3.86 |
2.49 |
ΔE |
2.15 |
2.16 |
2.12 |
2.38 |
1.54 |
Light resistance index ΔYI/Y (GPa-1) |
0.507 |
0.490 |
0.531 |
0.622 |
0.400 |
Light resistance color change index ΔYI/ΔE |
1.60 |
1.57 |
1.58 |
1.62 |
1.62 |
[Table 2]
|
C. Ex. 1 |
C. Ex. 2 |
C. Ex. 3 |
C. Ex. 4 |
C. Ex. 5 |
C. Ex. 6 |
C. Ex. 7 |
Polymerization ratio of polyamide-based polymer |
Diamine compound (molar ratio) |
TFMB 100 |
TFMB 100 |
TFMB 100 |
TFMB 100 |
TFMB 100 |
TFMB 100 |
TFMB1 00 |
Dianhydride compound (molar ratio) |
- |
BPDA 3 |
6-FDA 7 |
Dicarbonyl Compound (molar ratio) |
TPC 95 |
TPC 80 |
TPC 5 |
TPC 72 |
TPC 71 |
IPC 95 |
IPC 25 |
IPC 22 |
IPC 5 |
IPC 20 |
Additive (content) |
- |
OP-1300A 500 ppm, Tinuvin 328 1.25 wt% |
- |
OP-1300A 500 ppm, Tinuvin 328 1.25 wt% |
Modulus (Y) (GPa) |
5.67 |
6.76 |
3.87 |
6.71 |
6.82 |
6.13 |
6.0 |
Transmittance (%) |
76.9 |
85.4 |
89.3 |
88.8 |
89.1 |
89.5 |
89.0 |
Hz (%) |
68.74 |
34 |
0.28 |
0.39 |
0.5 |
0.6 |
0.7 |
Before light resistance test |
YI0 |
26.78 |
21.99 |
3.55 |
2.97 |
2.12 |
1.97 |
2.45 |
L∗ |
83.92 |
89.94 |
95.47 |
95.24 |
95.01 |
95.50 |
95.11 |
a∗ |
1.48 |
0.14 |
-0.22 |
-0.19 |
-0.55 |
-0.11 |
-0.50 |
b∗ |
12.81 |
10.94 |
1.96 |
1.64 |
1.33 |
1.09 |
1.50 |
After light resistance test |
YI |
35.39 |
28.97 |
6.33 |
7.54 |
6.64 |
7.74 |
6.97 |
L∗ |
84.05 |
89.89 |
95.61 |
95.49 |
95.19 |
95.56 |
95.16 |
a∗ |
0.60 |
-0.78 |
-0.75 |
-0.95 |
-1.18 |
-0.89 |
-1.05 |
b∗ |
18.09 |
15.96 |
3.67 |
4.41 |
3.96 |
4.49 |
4.13 |
ΔYI(YI - YI0) |
8.61 |
6.98 |
2.78 |
4.57 |
4.52 |
5.77 |
4.52 |
ΔE |
5.35 |
5.10 |
1.80 |
2.88 |
2.71 |
3.49 |
2.69 |
Light resistance index ΔYI/Y (GPa-1) |
1.519 |
1.033 |
0.718 |
0.681 |
0.663 |
0.941 |
0.753 |
Light resistance color change index ΔYI/ΔE |
1.61 |
1.37 |
1.54 |
1.59 |
1.67 |
1.65 |
1.68 |
[0244] Referring to Tables 1 and 2, the films of the Examples having a light resistance
index adjusted to 0.660 GPa
-1 or less according to the embodiment had excellent modulus and superior light transmittance
and haze compared to the Comparative Examples having a light resistance index falling
outside the range of the embodiment. Further, they were reduced in the rate of change
in yellow index and the color difference before and after the light resistance test,
confirming that the deterioration in optical properties and the color change due to
UV rays were effectively prevented.
Explanation of Reference Numerals
100: |
polyamide-based film |
|
|
101: |
first side |
102: |
second side |
200: |
functional layer |
300: |
cover window |
400: |
display unit |
500: |
adhesive layer |